When the New York Mets take on the Kansas City Royals tonight, it’ll be the first time two expansion teams have squared off in the World Series.

In most sports, “expansion team” means an organization that was founded in the previous few years. But baseball purists apply the term to any team founded after 1903, the first season the older National League recognized the upstart American League as its equal.

Until 1969, the club with the best record in each league would meet in the World Series; a tie for first would be resolved with a one- or three-game tiebreaker, depending on the league.

Original American League clubs

Boston Americans – became the Red Sox in 1908

Chicago White Sox

Cleveland Naps – originally named after player-manager Nap Lajoie, renamed the Indians in 1915

Detroit Tigers

New York Highlanders – renamed the Yankees in 1913

Philadelphia Athletics – moved to Kansas City in 1955, then to Oakland in 1968

St. Louis Browns – relocated as the Baltimore Orioles in 1954

Washington Senators – relocated as the Minnesota Twins in 1961

Original National League clubs

Boston Beaneaters – several different names (Doves, Rustlers, Bees) before becoming the Milwaukee Braves in 1953; moved to Atlanta in 1966

Brooklyn Superbas – settled on [Trolley] Dodgers in 1932, moved to Los Angeles in 1958

Chicago Cubs

Cincinnati Reds – known as the Redlegs from 1954 to 1959

New York Giants – moved to San Francisco in 1958

Philadelphia Phillies

Pittsburg [sic] Pirates – added the ‘h’ soon after

St. Louis Cardinals

Early expansion

In 1959, a group headed by lawyer William Shea announced plans to form a third major league, the Continental League. Shea’s main goal was to create a new franchise in New York to replace the Giants and Dodgers, who had relocated to the west coast in 1958. In doing so, he co-opted several cities that did not have teams, including Minneapolis and Houston.

The established major leagues responded by promising an expansion, particularly targeting cities that did not already have teams.

Washington Senators (AL) – replacement for the team of the same name, which had just moved to Minnesota; this team became the Texas Rangers in 1972

You might notice this created an imbalance: the American League now had ten teams, versus the National League’s eight.

Until 1997, MLB did not allow interleague play; the only time the AL and NL would meet on the field was in the World Series. Thus, both leagues always had to have an even number of teams.

The following year, the NL added two teams:

Houston Colt .45s (NL) – renamed the Astros in 1965, when they moved into the Astrodome

New York Mets (NL) – short for Metropolitans; for 45 years they played in Shea Stadium, named for the aforementioned lawyer

Divisional Era

In 1969, MLB added four more teams:

Kansas City Royals (AL) – a replacement for the Athletics, who had moved to Oakland before the prior season

Seattle Pilots (AL) – became the Milwaukee Brewers after just one year

Montreal Expos (NL) – relocated to Washington, D.C. in 2005

San Diego Padres (NL)

Each league now had 12 teams, so each split into two Divisions: East and West. The winners of each division would meet in a five-game “League Championship Series” to win the pennant.

That year, the “Miracle” Mets, then in their eight season, became the first expansion team to win a pennant – as well as the first team to win the World Series.

When the Senators moved to Texas in 1972, they swapped divisions with the Milwaukee Brewers; the Brewers had been in the AL West, since they started in Seattle.

That was the last move for several decades. There were two more rounds of expansion in…

…1977:

Seattle Mariners (AL)

Toronto Blue Jays (AL)

… and 1993:

Colorado Rockies (NL)

Florida Marlins (NL) – rebranded as the Miami Marlins in 2012

Wild-card era

In 1994, each league added a Central Division. To avoid giving any byes in the postseason, the second-place team with the best record would qualify as a wild card. (Or, as Alex Trebek often puts it, the highest scorer among non-winners.)

Until 2012, the wild card would play the team with the best record – unless both teams were from the same division, in which case the wild card would play the team with the second-best record. Now, the two top wild-card teams play in a single-game playoff, and division rivalries are ignored for seeding purposes.

Sadly for 9-year-old me, and millions of other baseball fans, a strike canceled the later stages of the 1994 season, including the postseason. It wasn’t until 1995, therefore, that we saw our first taste of what is called the Division Series – the “League semifinals,” in other words.

The most recent expansion came in 1998:

Tampa Bay Devil Rays (AL) – removed “Devil” in 2008

Arizona Diamondbacks (NL)

To keep even numbers in both leagues, the Milwaukee Brewers (which just happened to be owned by Commissioner Bud Selig) flipped to the National League. The Detroit Tigers also moved from the AL East to the AL Central.

The Milwaukee Brewers are the only team that has been in four different divisions.

Rebalancing act

At this point, the NL had 16 teams (6 in the Central) while the AL had just 14 (4 in the West). As interleague play became more accepted (remember, purists are rather set in their ways!), the idea of balancing the number of teams in each league became more realistic.

The Houston Astros moved from the NL Central to the AL West in 2013, evening the leagues at 15 teams apiece, and the divisions at 5. (Other than the Brewers, the Astros are the only team to have been in three different divisions.) Because of the odd numbers, interleague play is necessary nearly every day of the season.

And now, a visual representation of each league from 1903 to the present day. For the sake of simplicity, I’m using only the current name for each club.

I think there are a few errors in that chart. The last year of two divisions per league was 1998 (which was also the Mark McGwire/Sammy Sosa home run race), and up to that realignment, the Cubs were in the NL West. I remember it because the Cubs ended the 1998 season tied with the Giants, resulting in a one-game playoff to decide the NL West winner before the playoffs proper could begin. (This gave Sosa an extra game in which to rack up more HRs, but he didn’t.)

That one game playoff was for the wildcard not a division title. He has it correct though technically the first divisional playoff occurred in 1981 when a strike interrupted the season and the first half division winners faced off against the second half division winners in a best of 5.

It was the only year the Expos ever made the post season and oddly enough the team with the best overall record in baseball that year didn’t make the playoffs.